Assuming prep work has been done to minimize paint defects, I would have to go with either:
1. Meguiar's #26 - very inexpensive, available OTC, and has a unique "darkening" quality. After all the boutique products I have tried, my wife *always* wants #26 on her red Focus.
2. Souveran Paste Wax - High in initial cost, but deep look is unmatched.
Just my $.02,
MCA